Supporters of bipartisan legislation to overhaul the nation’s toxic chemicals law hope to use a committee hearing Wednesday to assuage a Senate chairwoman’s concerns that the proposal would usurp tougher state environmental laws.

A compromise (S 1009) reached this spring between the Senate Environment and Public Works Committee’s top Republican, David Vitter of Louisiana, and the late New Jersey Democrat Frank R. Lautenberg would require an assessment of the dangers posed by all actively used chemicals and prioritize regulations based on the potential risks to human health. The EPA could then take a variety of actions upon finding that a chemical is unsafe, including requiring labeling to warn consumers about hazards and phasing out or banning the sale of dangerous products.

Supporters hope the compromise will serve as a template for legislation that would overhaul the Toxic Substances Control Act (PL 94-469) for the first time since it was enacted in 1976. The measure is the only major environmental law never to be significantly revised, and the EPA has struggled to oversee more than 84,000 chemicals used in commerce.

Lautenberg had been trying to overhaul the law for years, and his deal with Vitter — who represents a state where the chemical industry is important to the economy — looked like a breakthrough.

But Environment and Public Works Chairwoman Barbara Boxer, D-Calif., staunchly opposes language in the bill that could pre-empt state authority to regulate or restrict chemicals used in commerce once the EPA acts on those substances. Boxer and other Californians fear the language could undermine rigorous chemical and environmental laws on the state’s books.

Senate aides said Tuesday that neither Lautenberg nor Vitter intended to usurp state authority on water, air or other environmental regulation. The only state actions they sought to limit, the aides said, were those affecting chemicals on which the EPA had made final safety determinations. Ensuring one federal system as opposed to 50 individual state approaches was crucial to getting industry and their Republican allies on board with the legislation.

New Mexico Democrat Tom Udall, a co-sponsor of the Lautenberg-Vitter bill, said in a statement he is committed to advancing the bipartisan legislation. He said his staff has been working with Vitter’s aides on “thinking through creative solutions” to some of the issues raised and is “optimistic” a solution can be reached.

“It’s a near-universal opinion that the current law is deeply flawed and must be updated so that it effectively does what Congress intended — protect Americans from dangerous chemicals,” he said. “Enacting major environmental laws is a very tall order, and we are closer than we’ve been in decades.”

Meanwhile, the attorneys general of nine states, including California, planned to send a letter Wednesday to Environment and Public Works Committee Democrats highlighting concerns about the bill’s effect on state enforcement powers.

“Our citizens are better served when states are allowed to complement the federal government’s efforts,” they wrote in the letter. “Innovative state laws often result in better regulation and more safeguards, particularly for vulnerable subpopulations such as children and pregnant women.”

Committee Democrats see the hearing as an opportunity to persuade Boxer to move the bipartisan compromise through committee — despite her earlier comments that it has no chance of passing in its current form through the panel.

Interests with a stake in the legislation say Boxer has committed to listening to their viewpoints before charting a path forward. She previously said the committee will hold hearings to examine several bills addressing chemical safety — including an earlier version of Lautenberg’s bill with only Democratic co-sponsors — as she develops a chairman’s mark.

Supporters of the compromise struck just before Lautenberg’s June 3 death say it represents the best starting point for action on a broad overhaul.

“It’s not very often you get the opportunity to work on major environmental legislation on a bipartisan basis,” said an aide to a committee Democrat.

A large coalition of public health, environmental and labor organizations called Safer Chemicals, Healthy Families opposes the Lautenberg-Vitter bill in its current form but has advocated for amendments to make the measure more acceptable to member groups. A handful of other organizations, particularly the Environmental Working Group, has taken a harder line against the legislation.

Aides know that changes will be necessary if the bill is to have any chance of advancing through committee and moving to the floor.

“This hearing could help to serve as a road map for how we can get the bill from where it is to a place where Sen. Boxer feels comfortable marking it up,” the Democratic aide said.